In the fabrication of semiconductor devices, such as light emitting diodes (LEDs), a process may include the generation of epitaxial layers on a virtual substrate, such as GaN (gallium-nitride) grown on a sapphire crystal (which may be referred to as a GaN-sapphire substrate). Upon completion of the fabrication of the layers on the GaN-sapphire substrate, the epitaxial layers may be etched between individual devices to singulate the devices.
Laser lift-off is the most common commercial approach for substrate removal in GaN-based devices. In this conventional operation, a laser with an appropriate wavelength is fired through the sapphire crystal, and light is absorbed at the sapphire/GaN interface. The laser operation causes local heating and delamination of the GaN from the sapphire. Further, electrochemical etch has been used for undercutting layers of GaN. Non-native sacrificial layers (such as ZnO—zinc oxide) have also been used to facilitate chemical lift-off.
However, the conventional fabrication process requires the singulation etching down to the sapphire surface of the virtual substrate, and the separation of the GaN material from the sapphire crystal. This processing limits the productive yield of the device fabrication, as well as limiting the possible geometry of devices that are produced.